Batteries are a stored energy source that has many useful and practical applications. When stored energy is released from a battery, an energy conversion process known as discharging will take place. When energy is re-loaded to a battery after discharging, an energy conversion process known as charging will take place. During charging and discharging, heat and gas are generated in a relatively confined volume. While batteries are a relatively safe, reliable and portable stored energy source, the heat and pressure generated during charging and discharging, and especially during rapid charging, rapid discharging, faulty charging or faulty discharging, the heat and pressure generated can be problematic and may lead to explosion in extreme conditions.
With the increasing demand for batteries having higher energy storage capacities so that battery-driven vehicles (“EV”) and battery driven apparatus such as mobile phones and portable computers can have longer operation duration before requiring recharging, the risk of “thermal runaway” in batteries also increases. Thermal runaway in batteries is undesirable and is typically accompanied by venting of combustible vapours, smokes, sparks and flame and is a safety concern for modern day battery operation.
Batteries having safety arrangements to prevent thermal runaway and to mitigate explosion risks are known. Example of such battery safety arrangements includes pressure-triggered devices such as safety vents and current-triggered devices such as fuses.
Sealed batteries having an over-pressure current interruption arrangement have been described in U.S. Pat. No. 5,418,082 & U.S. Pat. No. 4,943,497. In such batteries, current connection between an electrode and a battery terminal is by a welded assembly. When the internal pressure of a battery reaches a predetermined threshold, a safety member operates to break the welded connection to terminate battery reaction.
Batteries having another type of over-pressure current interrupting arrangement are also taught in U.S. Pat. No. 5,750,277. In this arrangement, current connection between an electrode and a terminal is formed by a resilient conductive member urging against another conductive member. When the internal battery internal pressure reaches a predetermined threshold, a safety member is deformed and operates to break the current connection, thereby interrupting current connection of the battery.
A lithium rechargeable battery described in U.S. Pat. No. 7,186,477 has an over-pressure protection header comprising a rupture disc (31) which is riveted with an annular weld plate (33) to form the current connection. When the internal pressure of the battery exceeds a threshold, the rupture disc will be popped up to break the current connection.
Known battery safety devices arrangements are not quite satisfactory. For example, in the welded type arrangement first mentioned above, a very high internal pressure is required to break the welded connection and therefore the current connection, since a large welded area is usually required to achieve a very low resistance. In the spring urged arrangement, the contact resistance can be variable and non-consistent during the life of a battery, and a battery incorporating such an arrangement would not perform well until a vibration test, which is required when a battery is to be put on the consumer market. In the riveted type arrangement of U.S. Pat. No. 7,186,477, a very high internal pressure is required to pop up the rupture disc if the contact resistance between the rupture disc and the annular weld plate is to be low.